Electrical utility service providers, or simply utilities, generate polyphase electrical power, and typically three phase power. Polyphase electrical power is alternating current (“AC”) electrical power that is supplied on a plurality of power supply lines wherein the voltage waveform on each of the power supply lines has a unique phase angle. While only a single phase of the polyphase electrical power may typically be provided for single family residences, true polyphase electrical power is typically provided to larger facilities such as commercial and industrial facilities.
Utilities monitor energy usage by customers through electricity meters. Electricity meters track among other things, the amount of energy consumed, typically measured in kilowatt-hours (“kwh”), at each customer's facility. The utility uses the consumption information primarily for billing, but also for resource allocation planning and other purposes.
Modern solid state electricity meters typically include microcontrollers and memory for sensing and storing various electrical usage parameters and metrics data. This data is stored in memory and can be referenced by service technicians and meter readers. Solid state electricity meters also attempt to store vital billing information, power line events, time stamps, and other metrics in a non-volatile memory once a power line outage is detected.
In the past, utility personnel physically observed meter data on mechanical counters or electronic displays. Modem meters still often include interfaces such as optical ports and displays for on-site observation by utility personnel. However, because meters are generally located at the facility of the utility customer, such methods of meter reading are labor intensive and expensive. Modem electricity meters attempt to facilitate remote access to meter data by providing optional communications devices.
Thus, many modem electricity meters include electronics modules having a measurement board and optional electronic assemblies such as on-board communications devices facilitating remote control and programming of the meter and remote access to data acquired by the meter. The measurement board typically includes the sensors, signal processors, microcontroller and memory for data acquisition and storage, also known as a metering system or circuitry. The measurement board also typically includes an on-board power supply providing power to the data acquisition and storage devices and the optional electronic assemblies.
Various types of remote meter reporting systems have been proposed and/or implemented in optional electronic assemblies. Optional communications devices may include relays programmable for KYZ, EOI, LC, DT A, power factor threshold alert and voltage threshold alerts and real time communications links such as are modems, RS-232, RS-485, radios and power line transceivers, or the like.
One problem with optional communications devices, and especially with wireless radio communications, in utility meters arises from the high power requirements of such devices. For example, wireless paging technology can require in excess of one amp of current at approximately eight to ten volts. This power requirement far exceeds the power requirement for the remainder of the meter circuitry. Typically, even more advanced polyphase electric utility meters only require substantially less than one amp of current. As a consequence, if the power supply in a utility meter is designed to accommodate the worst case load anticipated due to the presence of wireless pager transmitters or other optional communications devices, the power supply must be drastically different, and generally much larger, then the power supply in the same utility meter without such optional communication devices.
The larger capacity power supply both occupies additional space within the meter and has increased cost. Because a utility meter is only required to perform these optional communication functions a very small fraction of the overall operating time of the meter, such additional power generating capacity goes unused for a substantial majority of the time. As a consequence, the relatively infrequent need for additional power does not necessarily justify the additional size, weight and cost issues that arise from the use of a large capacity power supply.
Data acquisition and storage hardware and communications hardware are both typically DC devices. The power supply in electricity meters converts AC power from the service line to DC power, some of which is stored in storage and smoothing capacitors. As previously stated, both the data acquisition and storage and optional communications modules require power for operation.
A typical onboard power supply utilized in electricity meters is a wide range switching power supply. A single wide range switching power supply may supply the power for both the data acquisition hardware and the communications hardware. Switching power supplies store DC energy in capacitors. The DC energy stored in the capacitors is typically used to sustain the operation of the microcontroller until the non-volatile memory write cycle is completed (approx. 400 mS) during power outages. The rate at which the DC energy is depleted from such capacitors upon interruption of the AC power varies significantly when communication devices are connected to the main power supply. For example, some communications devices could draw up to 250 mA dc during bursts of 100 mS and remain idle during several seconds. During start-up, shutdown, heavy load periods or loss of service, the energy stored in the capacitors can be used by these communications devices before critical data is stored resulting in a loss of critical data.
In some electrical devices, load management has been implemented in the peripheral circuitry which incorporated a load control circuit to reduce the peripherals power consumption during line power outages. When load management is not provided in an electricity meter, excessive capacitive loads added by external peripherals during the initial startup disturb the power supply operation e.g. the switcher does not start up because the over-current protection is tripped. However, when separate load control circuitry is provided for each peripheral device, the additional expense can be cost prohibitive. Load management seeks to disconnect the communications devices when insufficient power is available to guarantee operation of data storage functions.
Those skilled in the art will recognize that the primary function of an electricity meter is to acquire and store data necessary to determine the electrical consumption. Providing communication for remote data acquisition and the like is a secondary function of electricity meters. Thus, should the power generated by the on-board power supply be insufficient to power both the data acquisition and storage hardware and the communications hardware, whether during start-up, shut-down heavy load periods or power loss, then it is preferable that power be supplied to the data acquisitions and storage hardware.
Thus, a need exists for a load management system which economically facilitates remote access to the functions of an electricity meter and the data stored therein while protecting the data from loss during outages or overload situations.